Earth and Environmental Science

2 December 2019

GEOL 5903 Seminar: Alicia Escribano
Title: "The great Toba Super-eruption; A Bottleneck for Mankind?"
Location and Time: Huggins Science Hall, Room 336, 12:30 p.m.
Abstract:
The Toba Caldera, located in northern Sumatra (Indonesia), has been the site of several large explosive eruptions over the past million years. The most recent Toba eruption (74 ky BP) is considered to be the largest terrestrial volcanic eruption of the Pleistocene (even larger than the Yellowstone super-eruptions).  This eruption ejected an enormous volume of material estimated between 2,800 and 5,300 km³ as well as an estimated 10¹⁵–10¹⁶ g of stratospheric dust and H₂SO₄ aerosols. Ice-core data and atmospheric modeling indicate a ca. 6 yr residence time for the dense global aerosol cloud. Such a stratospheric aerosol loading is predicted to have caused a “volcanic winter” with possible abrupt regional cooling of up to 15° C (similar to nuclear winter scenarios), and global cooling of 3–5° C (and possibly greater) for several years. Genetic studies link the Toba event with a severe human bottleneck that occurred sometime prior to ca. 60,000 years ago, when the number of modern humans dropped cataclysmically, and humans evolved from the few thousand survivors of whatever befell humans in Africa at the time.  Counter arguments rely on a poor climatic effect of the Toba winter on vegetation and mammals. The recent discovery of microscopic glass shards characteristic of the Toba Tuff in the south coast of South Africa; a region in which there is evidence for early human behavioural complexity, suggests that humans in this region thrived through the Toba event and the ensuing full glacial conditions.